It found that results for the bottom 10 per cent of students have fallen one-and-a-half times as much as those in the top decile.

"Kids at the top end of the system have better access to teacher coverage, better access to resources, and better access to curriculum subjects that offer higher tertiary entrance scores," Mr Hetherington said.

"So all these things come together to create widening inequalities in performance. No-one is quarantined from that. It touches all of us into the future."

Australia's PISA scores in maths have declined by almost 6 per cent since 2000.

The Deloitte report said PISA maths scores were found to have the largest impact on economic growth, and increasing test scores correlated with higher wages, capacity to innovate, and higher levels of education.

Economist Chris Richardson said education was one of the most important drivers of economic growth in the future economy.

"Ultimately if you want the Australia of the future to be prosperous, it has to be highly skilled," Mr Richardson said.

"We have to get our education system right, and at the moment there are some worrying trends."

'You need to address both sides of the equation'

The Public Education Foundation's Mr Hetherington said approaches like that of Ashcroft High School should be considered by other schools.

"You need to address both sides of the equation. You need to have the recognition that deprivations are occurring for particular kids, and then schools need to have the resources to address them. That's why needs-based funding is so important."

Mr Hetherington said the quest to close the inequality gap was urgent.

"Education is a bit like the proverbial oil tanker in that any changes take a long time to develop and implement," he said.

"That means that we need to get started immediately, because whatever we do now will take years, decades even to work its way through the system. We don't have time to lose."